Using Vitek MS v3.0 To Identify Nontuberculous Mycobacteria in Liquid Media in a Clinical Microbiology Laboratory

Abstract

ABSTRACT Recently, the incidence of diseases caused by nontuberculous mycobacteria (NTM) has been increasing worldwide, especially in immunocompromised patients and those with potential chronic lung disease. Vitek MS v3.0 matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) has emerged as a rapid and reliable method for identifying mycobacteria in clinical laboratories. This study aimed to evaluate the performance of Vitek MS v3.0 by isolating NTM directly from automated liquid medium systems using patient samples. A total of 855 Mycobacterium growth indicator tube (MGIT)-positive liquid cultures were investigated. Among them, 658 (77.0%) liquid cultures were correctly identified to the species, group, or complex level, 192 (23.0%) resulted in no identification, and 5 (0.6%) were misidentified at the species level. DNA sequencing identified 855 NTM isolates from liquid cultures, comprising 316 isolates of rapidly growing mycobacteria (RGM) and 539 isolates of slow-growing mycobacteria (SGM). Using the Vitek MS system, the RGM integral identification rate (276/316 [87.34%]) was higher than the SGM rate (381/539 [70.69%]) (P < 0.01). It was also higher than the SGM rate for all MGIT report-positive periods. These results indicate that the Vitek MS v3.0 system can rapidly identify NTM species from liquid cultures. Further validation using molecular techniques is required. IMPORTANCE Rapid and accurate identification of nontuberculous mycobacteria (NTM) is essential for diagnosis, appropriate therapy, and infection control. Vitek MS v3.0 matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) has emerged as a rapid and reliable method for identifying mycobacteria in clinical laboratories. This study reported a clinical validation of the Vitek MS V3.0 system for identification of NTM isolates from 855 MGIT-positive liquid cultures which contained relatively large NTM types. Vitek MS v3.0 showed a promising rate for identification NTM isolates in positive liquid cultures. Vitek MS v3.0 had a better performance with RGM than with SGM. Vitek MS v3.0 results included “unidentified” or “misidentified” NTM isolates, which would also serve as an important reference for future optimization of this system. Vitek MS v3.0 represented a valuable technique for NTM identification from positive liquid cultures.

Keywords

• liquid media
• MALDI-TOF
• mycobacteria
• identification